The single biggest item that contributed to my shooting improvement? That's easy: A COMMITMENT TO EXPERIMENTATION.
Archers come in all sizes, shapes, ages, degrees of physical conditioning, levels of hand/eye coordination, etc., etc.
What works for one person (or many) will not work for others.
EXPERIMENT . . .
Try split finger, 3-under, 2-under, etc.
Try anchoring all over your face: on an eye tooth, under your cheekbone, under your eye, etc. The only real requirement is that your anchor be reproducible every time.
While avoiding a death-grip on your bow, experiment with everything right down to a "shaking hands with a baby" grip.
Try bows with a high-wrist, medium-wrist, low-wrist, and extra low-wrist grips.
Experiment with a pull-through release and with what's commonly called a "dead release."
Try recurves of varying lengths, draw-weights, and design. Same for longbows.
Play with wood, aluminum, and carbon arrows. Vary their weight and maybe even their length.
Ask other archers for advice but don't commit to something because it works for them. It's what works for YOU that counts!
This all takes time, lots of it. But that's part of the fun of archery.
Mark